When I make this, I start the water for the pasta first, then boil in heavily salted water it as I'm making the sauce. When the pasta is ready to drain, reserve 1 cup (give or take) of the cooking liquid right before dumping the pasta.
For the sauce, add the bacon to a large cold skillet and turn the heat to medium. Render the fat in the bacon and let it brown slightly - it won't be totally crispy at this point.
When the bacon is about halfway to crispy, add the mushrooms and cook with the bacon for 5-7 minutes or until the mushrooms have released their liquid and browned at the edges.
Add the onion and crushed red pepper flakes (if using) and stir into the skillet for 3 minutes to soften slightly.
Add the garlic and salt and stir for one minute (the garlic should just barely cook), then add the crushed tomatoes.
Reduce the heat to medium-low and let the tomato sauce simmer for 10-15 minutes while you finish the pasta. Taste the sauce and add more salt if you'd like; it should be very flavorful.
Combine the pasta with the sauce and add the cream and parmesan cheese to the skillet. Toss everything together with ½ cup of the reserved cooking liquid and taste again for seasoning; keep adding pinches of salt until it's just right.
Serve. Devour. Enjoy!